1. The Field of the Invention
The present invention is directed to methods and apparatus for enhancing the performance of visual display units which utilize plasma display panels. More specifically, the present invention provides methods and apparatus for providing an accessory device for positioning in front of the viewing surface of a plasma display panel that suppresses near-IR emissions in the range of about 800 to about 2500 nm while simultaneously providing good photopic transmittance and enhanced color and display readability.
2. The Relevant Technology
Many types of visual display units (VDUs) are known. A very useful type of flat panel display for VDUs utilizes a plasma display panel (PDP) to generate the visual image. PDPs consist of individual cells at the intersection of typically orthogonal electrically communicating address lines. The individual cells electrically communicate with a gas plasma. In a typical PDP, the conducting electrodes are patterned onto opposed surfaces of a front and a rear substrate material. The address electrodes are typically patterned onto the front-facing surface of the rear substrate material and the sustain and bus electrodes are patterned onto the opposed, i.e., rear-facing, surface of the front substrate material. The substrate material is usually glass. Phosphor material(s), similar to that used in fluorescent lamps, are deposited onto the electrode-patterned, front-facing surface of the rear substrate. The phosphor materials can be individually chosen such that they emit only red, green, or blue light thus providing the ability to produce a colored image. Electrically isolating separators are positioned between the different phosphor materials to form separate phosphor channels. The gas plasma is contained between the phosphor materials deposited on the rear substrate and the opposed surface of the front substrate. In this configuration, when a sustaining voltage is applied to the sustain electrodes, the fringing fields from these electrodes reach into the gas plasma and create a discharge resulting in the emission of ultraviolet (UV) light from the gas plasma. The UV emission, in turn, excites the adjacent phosphor material resulting in emission of visible light which is transmitted through the electrode-patterned front substrate and, thus, to the eye of the VDU user.
A problem with PDPs is low luminous efficiency, a measure of the display output light luminance for a given input power. Although typical fluorescent lamps emit about 80 lumens of light for every watt of electrical power supplied, current PDPs emit only about 1-4 lumens per watt. In order to achieve sufficient brightness, relatively high power input is necessary. The high power input, however, results in the emission of significant electrical noise including, specifically, radio frequency interference (RFI) due to the plasma discharges and significant infrared (IR) energy due to the plasma discharges and the heat generated within the panel. The RFI and IR emissions may cause interference with other electronic equipment in the near vicinity of the PDP. In particular, the IR radiation can interfere with remote control devices which typically operate at wavelengths in the near-IR range. Thus, there is a need to reduce the emission of radio noise and IR energy from PDPs.
Another problem with PDPs is that the inherent spectral, i.e., color, properties often interfere with good display readability. Various PDPs manufactured by assorted manufacturers comprise different phosphor materials and differing configurations of the components such that the spectral properties of the PDPs differ somewhat. The use of color filters to compensate for the inherent spectral properties and permit clear and readable color images is well known. In particular, depending on the inherent spectral properties, different PDPs may be chromaticity-enhanced with various colors, i.e., tinges, used as a filter. For example, one manufacturer may desire a device having a purple tinge for color correction while another may desire a blue- or green-tinged device for color correction of their PDP.
Various optical coatings and dyed materials are known that can reduce radio noise and IR emissions as well as provide color correction for PDPs. In some cases, however, these optical coatings and dyed materials are not compatible with the production and assembly processes used for PDPs. In addition, many of these optical coatings and dyed materials, especially when provided on an outer, or otherwise environmentally exposed, surface of a PDP, suffer from low durability. Another problem is that the various optical coatings and dyed materials may cause decreases in the photopic transmittance of the PDP which worsens the readability of the display.
It would be an advance to provide methods and apparatus for providing an accessory device for suppressing electrical noise emissions, specifically RFI and near-infrared radiation, and for enhancing the chromaticity of the display while, simultaneously, maintaining good photopic transmittance. It would be a further advance to provide methods and apparatus for providing electrical noise suppressing/chromaticity enhancing accessory devices for PDPs that are cost-effective and highly durable.